Nearly every electronic device today contains some sort of memory, or electronic storage media, for storing data. This memory is typically implemented in hardware using addressable semiconductors, i.e., integrated circuits consisting of transistors. There are many different types of memory used in modern electronics, including, but not limited to, RAM, ROM, Flash, and EEPROM.
Elements in semiconductor integrated circuit devices have been miniaturized more and more as the degree of integration of the devices has increased. As sizes of MOS transistors (insulated gate type field effect transistors) decrease, thicknesses of gate insulating films decrease, and thicknesses of interlayer insulating films between interconnections also decrease. Therefore, if an external supply voltage having a conventional value of, for example, 5 volts is used as an operation supply voltage, dielectric breakdown may occur, impairing the reliability of the integrated circuit device. Therefore, in a semiconductor integrated circuit device such as a semiconductor memory device that is utilized in a system operating with a conventional supply voltage value of 5 volts, the external supply voltage is stepped down or is subjected to voltage down conversion to generate an internal voltage. The internal voltage then is utilized within the system as an operation supply voltage.
An internal voltage generator, which may down-convert for generating the internal voltage, is designed such that the internal voltage generated by the internal voltage generator can maintain a level of a predetermined constant voltage value, even if the external supply voltage becomes higher than the constant voltage value. An operation for maintaining an internal voltage at a constant voltage value is referred to as an “internal step-down” or a “voltage down conversion.” Such internal voltage generators are usually provided in semiconductor memory devices such as DRAMs (dynamic random access memories) and SRAMs (static random access memories). The reason for this is that logic LSIs (large-scale integrated circuit devices), such as microprocessors which determine system power supplies, have not been highly miniaturized as compared with semiconductor memory devices, and a voltage of 5 volts is still used as the system supply voltage. The purpose for the step-down is to ensure the reliability of the internal circuits of the integrated circuit device and to reduce the consumption of current. The power consumption is generally proportional to the square of the voltage. Therefore, a lower operation supply voltage enables lower power consumption.